The present invention relates to fire alarm systems and particularly to a unique code transmitter for use with a type of fire alarm system that involves a so-called McCulloh loop circuit.
The device and associated apparatus of the present invention is readily adapted to serve with presently available low voltage fire alarm systems. These systems are typically electrically supervised, zoned, local fire alarm systems with provisions for transmitting a coded signal over a base loop circuit to a central fire headquarters. Also, such systems typically receive alarm signals from remote monitoring units which are connected into electrically supervised initiating circuits and provides audible and visual indications of such conditions.
One of the important functions of the aforedescribed fire alarm system is to operate an alarm to energize or de-energize control equipment for other electrical systems in the building. Typical examples of application are for the purpose of turning off ventilating or airconditioning systems, automatically closing fire doors, etc., when an alarm is sounded.
There are generally three basic modes of operation of the system described above: the supervisory or normal condition; the ALARM condition; and the TROUBLE condition. In addition, such a system can also include facilities for a so-called "test" condition. The way in which such a system operates is that when 24 volt AC power is applied, with no alarms in progress and the TROUBLE signal silent, the system is in the supervisory mode of operation, this being the normal condition. As long as this condition prevails, the system requires no attention or routine servicing.
In the ALARM mode of operation, the sounding of a continuous general evacuation alarm results from the pulling down of a box lever at any manual box station or the operation of any automatic fire detector. Alarm signals continue until the station or detector from which the alarm originated is restored to the normal condition and the reset button on the control panel is pressed. Simultaneously with the sounding of the general alarm, a four round coded signal is transmitted over a base loop circuit to a central fire headquarters and the trouble signal sounds continuously. Concurrently a fan shut-down relay is energized such that its contacts function to energize or de-energize other electrical circuits in the building such as ventilating, airconditioning, etc.
The TROUBLE mode of operation eventuates when any electrical fault develops in the system that would prevent the sounding of an alarm. In such case the system TROUBLE signal sounds a continuous trouble warning signal and one round of TROUBLE code is transmitted over the base loop to the central fire headquarters.
Forming part of the aforenoted system is a code transmitter which is a spring driven, electrically released mechanism capable of transmitting 40 full rounds of code on one full winding of spring. The coding mechanism consists of a spring driven clock escapement that, through appropriate gearing, drives a coding wheel and a face cam at a five to one ratio. The escapement mechanism is controlled by two interconnecting arms, one actuated by the trip coil, the other by a pawl riding into and out of detents in the cam. Complete details on such a code transmitter may be obtained by reference to the aforenoted Catalog No. 1308 of the Edwards Company.
The code transmitter functions in connection with a McCulloh loop circuit, such circuit providing for the ability of the system to receive an alarm, even though the fire alarm circuit may be open because of some fault in the box circuit wiring. Such McCulloh loop circuit will be described in some detail hereinafter. Suffice it to say at this point that the technique of the McCulloh loop circuit is to provide operation even though there is an open, by using the remaining good leg of the circuit and ground return.
The response at the control panel to a fault can be either automatic or manual. When automatic, relays perform the conditioning function; when manual, a switch must be manually operated. The automatic grounding type system is free of circuit grounds until a break occurs. The relays then de-energized on both sides of the line are tied together (via the relay contacts) at the positive terminal of the power supply. At the same time, the negative side of the power supply is grounded. In the event of an alarm under these existing conditions, the fire alarm box mechanism will transmit its signal from the positive line via the signaling contacts to the signal responsive devices at the control panel through ground return to the negative power source. Both boxes and the central control panel must be designed for and be compatible with this type of operation under an open circuit fault.
Although the above described schemes and arrangements involving McCulloh loop circuits and the like have their purposes and uses, it has become desirable to provide greater flexibility in the performance of fire alarm systems and more specifically to allow for field programmable arrangements such that the modes and types of operations and the particular character of code signals can be altered or modified by the customer.
Accordingly, it is a primary object of the present invention to provide an extremely flexible code transmitting apparatus or system which eliminates the mechanical parts involved in code transmitters heretofore known, particularly avoiding the need for winding up a spring actuated device.
Another primary object of the present invention is to avoid the ambiguity that is often present when a variety of alarm or trouble conditions occur simultaneously or with only a very slight time gap between their occurrences such that the code signals generated by a first condition can be confused with those generated by a second condition. In other words, the coded signals of the present invention which define particular individual modes and combinations of modes of operation are clear and unambiguous and allow the operator at a central headquarters to identify without doubt the particular condition to which the system is responding.
Another object is to enable the system to shift to particular priorities, that is, for example, to give precedence to one transmitter over another; or to indicate a particular condition such as an ALARM condition which should take priority over, for example, a TROUBLE condition, and to do this immediately, without having to wait for a mechanical code transmitter to go through its entire cycle.
Another object is to reduce the cost of the code transmitting system by fully implementing such a system with integrated circuits and the like which have been reduced substantially in cost in recent years.
In fulfillment of certain of the above stated objects, a primary feature of the present invention resides in the provision of a unique relay contact/diode arrangement for connection to the McCulloh loop circuit. This arrangement takes the place of the former mechanical type of code wheel or code mechanism.
A further feature of the present invention resides in the provision of a generated code for pulsing the relay contact/diode arrangement within the loop such that multiple code transmitters can be operated over the same McCulloh loop.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.